A GLA-Protein found by us in tumor microsomes is suspected of participating in nuclear synthesis and/or processing of rRNA in as much as warfarin, which we know is bound to these microsomes, also inhibits the synthesis of tumor rRNA. Furthermore warfarin inhibits rRNA synthesis in cultured human malignant cells and simultaneously affects some aspect of their cell cycle kinetics. Possible warfarin inhibition of synthesis of this GLA-protein, and reversal by vitamin k, are under study in both animal tumors and cultured cells. Effort will be made to correlate these phenomena with disturbances of various steps in ribosomal assembly in the animal tumors, and in suspension cultured HeLa cells. These experiments will then be performed with synchronized HeLa suspension cultures to investigate possible function of the GLA-protein in control of progression through the cell life cycle.